Some types of dump trucks that travel in mines are known as the series hybrid type. Such series hybrid type dump trucks generate electric power with a generator driven by the engine and supply the electric power to rear wheel motors for driving the rear wheels. By taking advantage of the electrical configuration of the series hybrid type, traveling technology based on the trolley system has been implemented. In the trolley-based traveling technology, trolley wires generally employed for electric trains are installed in prescribed climbing sections. In the climbing sections with trolley wires, a vehicle having power collectors (provided on the vehicle to be movable up and down) travels not by using the electric power supplied by the engine and the generator but by using electric power acquired from the trolley wires by elevating sliders of the power collectors to be in contact with the trolley wires (hereinafter referred to as “trolley traveling”). An example of the trolley-based traveling technology has been described in Patent Literature 1, for example. In this case, the drop in the traveling speed in the climbing sections (equipped with the trolley wires enabling the trolley traveling) can be avoided since the electric power supplied from the trolley wires is greater than the electric power generated with the engine power.
Meanwhile, there exists a conventional technology detecting the lane (for the traveling of the vehicle) and controlling the vehicle to prevent the vehicle from deviating from the lane based on the result of the detection, as described in Patent Literature 2. This technology is pertinent to the traveling technology of automobiles. Images of the road surface are shot with a camera or the like and lane markers (white lines, Botts dots, etc.) corresponding to the lane are extracted from the images by image processing. The control of the vehicle is executed by adjusting the steering and the driving/braking force so that the vehicle travels between the extracted lane markers. Imaginary offset lane markers are set a prescribed distance inside the lane markers (area to be judged as the lane) exclusively in prescribed sections, and a control value is increased as the vehicle deviates outward from the lane marker.